The present invention relates to a signal processing system for absolute-value sensors with periodic structures, particularly for position and angle sensors, in which, within a periodic structure, there is a measurement surface which is divided into several measurement sections and lies opposite at least one probe. Each measurement section represents a position marking, inputs to the periodic sensor structure are cyclically connected via a switch input group to a signal source, and outputs of the periodic sensor structure are connected to an evaluation circuit.
Highly accurate sensors for the precise determination of geometrical values, and which are stable for a long time are based on the principle of scanning periodic structures, which can be designed as a very stable reference scale. This principle is employed in incremental or coordinated path, position or angle-of-rotation sensors.
Systems which operate in accordance with the foregoing electronic inquiry principles are known. An example of such a sensor is described in U.S. Pat. No. 4,733,235 of J. A. Baer, et al wherein AC signals are applied successively to electrodes of a bank of electrodes capacitively coupled to electrodes of a second bank positioned at a different pitch to provide a vernier displacement measurement system.
The periodic sensor, under consideration in the case of the present invention, is cyclically controlled via a multiplexer which, in its turn, is excited by an oscillator of predetermined amplitude. Scanning control signals cause the multiplexer to switch the oscillator signal in succession solely to, in each case, one measurement surface.
The information-bearing parameters are, in this connection, coded in the signal amplitude, which is susceptible, however, to the influence of external noise signals. Thus, additional measures are necessary in order to suppress the noise signal.
For the detection of n positions, an equal number of switches and at least n electric connections on the sensor element are necessary. The measurement surface itself is divided into several measurement sections.
The disadvantage is that, after every intended or unintended interruption of the supply voltage, a zero position must first of all be employed in order to detect the instantaneous absolute position of the object being measured at the time of connection. Only then can each further change in position be detected by counting the periodic markings of the sensor element which are passed over by the probe in the sensor.